It is now common place to mark articles with identifying indicia particularly bar codes. These are digital codes utilized to identify articles. The bar code is usually identified with a laser scanner. In order for this to properly identify the bar code, the bar code must be printed very precisely. In many applications this is relatively simple. The bar code is simply printed onto a label which is adhered with a pressure sensitive adhesive to the article being identified.
In other applications this is very difficult, particularly with cured rubber articles. Generally, such cured rubber articles have irregular surfaces. When these products are formed and cured, the surface simply is not as smooth as, for example, a molded thermoplastic article. Further, it is very difficult to adhere something to a cured rubber article due to the plasticizers and oils in the rubber. Adhesives generally fail after a period of time. This problem is further exacerbated by the harsh conditions which these articles encounter. Typical cured rubber articles include tires and other automobile parts which are exposed to all types of environmental conditions from -40.degree. F. up to nearly 200.degree. F.
There are many different systems used to provide bar code identification using heat transfers. Mahn U.S. Pat. No. 4,610,904 discloses such a product. However, this will not adhere adequately to a rubber surface. Due to the design of the disclosed product, the bar coding would have to be screen printed. Screen printing is suitable when thousands of the same product are being produced. But when individual bar codes are required it is commercially infeasible. Mahn U.S. Pat. No. 5,413,841 discloses a heat transfer bar code. This uses a sublimation dye transferred into a thermoset layer. Again, this product will not bond to a rubber surface. However, applying the sublimation dye does facilitate printing the individual bar codes.
Mahn U.S. Pat. No. 5,380,391 discloses a heat transfer which is designed to bond to a rubber surface. This uses a cured rubber base material which is in turn marked with a contrasting solvent dye which provides the bar code. The article is overcoated with a protective thermoset layer and the product bonded to the rubber article during the curing process of the rubber article. This is simply placed on the surface of an article which is placed into a mold and cured. The heat and pressure from the curing process bonds the cured rubber based material to the article being marked.
This is good but the base material has an irregular surface. This requires application of the bar code using an ink jet printer or offset printing. It simply is not as crisp or clean as required to be properly readable. Further, the irregular surface of the rubber based material reduces the clarity of the printed bar code. This increases the likelihood of the scanner being unable to properly discern the number from the bar code.